The modern aircraft lavatory uses the flow of disinfectant fluid or a powerful pump to remove waste from a toilet into a waste holding tank. During ground maintenance the waste tank is emptied and sanitized. Sanitation is especially important to kill any infectious disease agents potentially carried in human waste. The emptying and sanitizing processes are typically performed by airport ground crews using a lavatory cart. The cart includes a supply of disinfectant fluid as well as a disposal tank. Disinfectant fluid is pumped into the aircraft waste holding tank after waste from the flight is drained.
In order to do an effective job of sanitizing the aircraft waste storage tank, it is desirable to fill the waste storage tank up to a specific level. Filling to a high level has many potential drawbacks if overfilling occurs. Overfilling can create spillage of disinfectant fluid, potentially contaminated with human waste. Spilled disinfectant fluid can freeze at high altitudes, creating solid projectiles, sometimes referred to as blue ice, which are potentially dangerous to the aircraft, especially its engines. Disinfectant fluid is harmful to the aircraft structure and electronics. Disinfectant fluid also includes a strong smelling detergent which when spilled on the interior of the aircraft via overfilling the toilet is objectionable, thus, it is desirable to minimize spills.
A valve which can automatically prevent overfilling of the waste holding tank is desired. An additional desire is to provide a valve with automatic shut off for use during the filling operation in combination with a backflow prevention device for use during normal operations.